1. Technical Field of the Invention
The present invention relates generally to apparatuses and methods for manufacturing electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.
More particularly, the invention relates to an apparatus and a method for shaping an electric wire for a stator coil of an electric rotating machine to form coil ends of the stator coil into a desired shape. Hereinafter, the coil ends denote the axial end portions of the stator coil which are located outside of slots of a stator core of the electric rotating machine.
2. Description of the Related Art
Generally, to increase the torque density of an electric rotating machine, it is necessary to improve the space factors of electric wires, which form a stator coil of the machine, by, for example, employing rectangular-cross-section wires as the electric wires. In addition, it is also necessary to minimize the coil ends of the stator coil which have almost no contribution to the generation of torque by the electric rotating machine. Further, the coil ends of the stator coil can be minimized by, for example, providing crank-shaped portions in the coil ends.
Japanese Unexamined Patent Application Publication No. 2003-264964 discloses a method of providing crank-shaped portions in the coil ends of a stator coil of an electric rotating machine. According to the method, an electric wire with a rectangular cross section is first shaped, using a first pair of male and female shaping dies, on a first plane to form a two-dimensional crank-shaped portion in the electric wire. Then, the electric wire is further shaped, using a second pair of male and female shaping dies, on a second plane which is perpendicular to the first plane to form a three-dimensional turn portion of the electric wire. The turn portion is to be located outside of slots of a stator core of the electric rotating machine and thus constitutes a part of the coil ends of the stator coil. The turn portion has a triangular overall shape and includes the crank-shaped portion at the apex thereof. Next, with the turn portion being held between the second pair of shaping dies, the electric wire is bent at each end of the turn portion using a female bending die, thereby forming a pair of straight portions of the electric wire. The straight portions are connected by the turn portion and to be respectively received in two slots of the stator core.
Conventionally, shaping dies used for shaping electric wires, including those disclosed in Japanese Unexamined Patent Application Publication No. 2003-264964, are made according to the desired finished dimensions of the electric wires.
For example, when a pair of male and female shaping dies is used to form a turn portion 92 of an electric wire which has a stepped shape as shown in FIG. 13A, the gap Wa between the shaping surfaces 91 and 90 of the male and female shaping dies is conventionally set constant over the entire length of the turn portion 92. In other words, the gap Wa between the shaping surfaces 91 and 90 for a straight part of the turn portion 92 is made equal to that for a bent part of the same. In addition, the gap Wa is also set to be equal to a desired finished width of the turn portion 92.
However, the electric wire may be an insulation-coated electric wire which includes an electric conductor and an electric insulator that covers the electric conductor. In this case, with the constant gap Wa, it is difficult to shape the turn portion 92 of the electric wire to have the desired finished width for all the parts of the turn portion 92 due to the expansion and contraction of the insulator during the shaping process. More specifically, on the bending outside of a bent part of the turn portion 92, the insulator is expanded in the length-wise direction and thinned in the width-wise direction of the turn portion 92, thereby lowering the withstand voltage of the electric wire. Consequently, during operation of an electric rotating machine, which includes a stator coil formed with the electric wire and other electric wires shaped in the same way as the electric wire, electric discharge may occur between those electric wires. On the other hand, on the bending inside of the bent part, the insulator is contracted in the length-wise direction and thickened in the width-wise direction of the turn portion 92, thereby bulging in the width-wise direction. Consequently, it is difficult to densely wind, in multiple layers, the electric wire together with the other electric wires shaped in the same way as it to form the stator coil of the electric rotating machine.
Furthermore, when the insulator is made of a thermoplastic resin which has already been crystallized and is thus hard, it is possible for cracks to occur in the insulator, thereby lowering the insulation performance of the insulator. On the other hand, when the insulator is made of a thermoplastic resin which has not been yet crystallized and is thus soft, the insulator tends to return to its initial shape after the shaping process, as indicated with arrows in FIG. 13B. Consequently, it is difficult to shape the turn portion 92 to satisfy the desired finished dimension thereof.